Existing cyclic fuel injected engines, i.e. compression ignition engines as represented by diesel engines, achieve a significantly higher thermal efficiency than spark ignition engines in automotive use and acceptable levels of carbon monoxide and light hydrocarbons. However, soot and nitrogen oxide levels are high. Various methods for reducing soot emission have been proposed. Such methods include optimization of combustion chamber shape, controlled injection of fuel, the use of catalytic exhaust gas converters and even modification of the fuel. All have failed to satisfactorily solve the problem. Similarly, methods proposed for control of nitrogen oxides have been similarly ineffective or have resulted in unacceptable losses in fuel economy.
Use of catalysts in engine combustion chambers has previously been proposed by others. For example, Bradstreet et al (U.S. Pat. No. 2,978,860) describe a catalyst based on rare earth oxides suitable for use in the combustion chamber of spark ignition engines. Similarly, Morotski et al (U.S. Pat. No. 3,684,743) teach the use of silico-alumina coatings on the combustion chamber walls of diesel engines and claims improved fuel economy. Note that the Bradstreet coating must not cause ignition of the fuel-air mixture otherwise ignition timing by spark control would not be possible, i.e. preignition or "knocking" would occur. The Morotsky coating is claimed to speed up the decomposition of fuel molecules during the preflame period and prepares th fuel for ignition, thus reducing the quantity of unsaturates in the liquid products of exhaust. Neither patent provides a coating suitable for vaporization and ignition of fuel in a fuel injected engine.
My issued U.S. Pat. Nos. 3,923,011 and 4,011,839 teach the use of catalysts positioned within the cylinders of pistont ype engines as does Haslett's patent U.S. Pat. No. 4,092,967. Although emissions and combustion efficiency are thus improved, the presence of a catalyst in the cylinder increases resistance to the flow of gases within the cylinder and thus pumping losses. Further, because catalyst is submerged in the gas flow path, the possibility of catalyst damage is increased.
As disclosed in my prior U.S. Pat. No. 3,928,961, surface reactions alone are far too slow to accomplish reasonably complete combustion in gas turbine systems let alone in internal combustion engines. Although the method of this patent can be used in internal combustion engines as per my two previously cited patents, the method of the present invention is far superior in that intimate admixtures of fuel and air need not be formed for contact with a catalyst. Such admixtures are very difficult to obtain in fuel injected internal combustion engines.
Methods of applying a catalyst to a surface, which are useful in the present invention, are known in the art. Examples are disclosed in Leak patent U.S. Pat. No. 3,362,783, Hindin patent U.S. Pat. No. 3,615,166 and Sergeys patent U.S. Pat. No. 3,903,020. The method of my U.S. Pat. No. 4,341,662 is an especially preferred method.
Methods, useful in the present invention, of applying thermal barrier coatings to the walls of internal combustion engine combustion chambers are also known in the art. For example, the methods disclosed in the U.S. Pat. No. 4,074,671 may be used.
Combustion of fuel in ordinary internal combustion engines is far too slow for maximum efficiency and may even require 40 to 50 crank angle degrees at certain engine speeds or as much as three or more milliseconds. About 20 crank angle degrees is typical for well-designed small engines. If combustion starts after top dead center, combustion will approach the constant pressure mode typical of diesel engines. As noted in the article of Kummer in the February 1975 issue of the MIT Technology Review, p 30, such combustion does not allow full expansion of the burned gases and results in loss of both fuel economy and engine power.
In spite of the fact that the Diesel cycle is considerably less efficient than the Otto cycle, existing Diesel cycle engines, i.e. compression ignition engines as represented by the diesel engine, achieve a significantly higher thermal efficiency than present spark ignition Otto cycle engines because diesel engines operate at higher compression ratios and do not need a throttled air intake. Diesel engines also have lower emissions of carbon monoxide and light hydrocarbons than do commercial spark ignition engines but have high emissions of soot and nitrogen oxides and usually will not burn alcohols as will spark engines.
It should be noted that spark ignition engines typically have a combustion burn time of about three milliseconds. Thus, although spark timing in spark ignition engines permits a closer approach to Otto cycle operation than is possible in diesel engines, combustion still requires about 20 crank angle degrees or more and typically exhibits considerable cycle to cycle variation as is shown in the figure on page 33 of the cited Kummer article. Accordingly, even the spark ignition engine departs appreciably from the Otto cycle requirement of heat addition at constant volume. In fact no conventional engine fully exploits the potential of the Otto cycle or even comes close to achieving theoretical Otto cycle efficiency.
For a compression ignition engine, such as the diesel, placing a catalyst in the line of gas flow, such as in a prechamber or in the main combustion chamber itself, offers only marginal improvement at best since turbulence and thus flame speed is reduced. This is confirmed by the reported results on a Haslett type engine published by Thring, p 133 of Platinum Metal Review, Vol 24 (1980). The need to improve fuel economy and catalyst durability are also noted.
Achievement of the full efficiency theoretically possible from an internal combustion engine requires combustion times nearly an order of magnitude shorter than even those of prior art spark ignition engines and a close approximation to true Otto cycle operation.